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Present situation and prospect of power lithium battery thermal management technology and methods are described in detail

Present situation and prospect of power lithium battery thermal management technology and methods are described in detail


First of all, let's do the first one is why do we have thermal management of batteries? In general battery system in the range of 15 to 35 degrees can achieve optimum power output and input, the largest comparable energy and the longest cycle life, 15 to 35 inside this is not a fixed value, because when I was just contact before, and listen to a lot of lectures, on a range of the data including the temperature there are inconsistent, Before have 0 to 60, 20 to 40, I was very confused, learn and looked behind also consulted some battery experts, they gave me a supply of a system is not the same, so the inside of the chemical reaction including material to the temperature of a catalytic phase is not consistent, so this is not a fixed interval, does not apply to each cell. But basically around 30 degrees, basically is a more appropriate, this is a case, the battery in different temperature range we normal to do paper strategy, is to do, according to the picture below normal temperature range 15-35 above said is fit in with the appropriate scope of work, once outside this range, So that's the green and the yellow in the middle and the diagonal in the middle and you have to limit the power.

If be beyond the outer ring basically does not allow the battery to allow again, as if in this interval, such as the temperature is lower than 15 degrees, such as in the below zero, can affect a charge and discharge capacity of the battery, if the temperature over high temperature in the storage and use of this kind of circumstance can affect cell cycle life, in the temperature directly affects the performance of the batteries, If say we have to ban or strategy or control was not well done, is beyond the scope, will lead to thermal runaway, the important reason is that some of the electrochemical catalytic negative reflect the overlay, leading to a sharp rise in the temperature including the inside of the pressure and temperature, the energy of sharp because we now encapsulation is basically like columns and side shell is basically a metal, The force is sufficient. Once the force is broken out, it is more terrible. Why do you say that the security performance of the soft package is better?

As mentioned in the battery PACK just now, the battery is usually composed of a series of multiple battery cells connected together. The battery is sensitive to temperature. If the temperature difference between the internal battery cells is too large, the battery will be uncontrolled and the performance of the PACK will be affected. The high temperature of batteries directly determine the life, the temperature is low absolute performance, the influence of temperature and temperature difference is also applicable to PACK, shall we carry out a thermal management, especially now with the enhancing the energy density, the use of high nickel system, high nickel system we also know, the higher the composition of the nickel, negative reflection threshold is lower, higher cooling needs.

New energy vehicles and traditional vehicles have always had a problem, charging time is relatively long, it is not so convenient to use, so now the requirements for fast charging, require you to charge a large ratio, resulting in increased heat, but also have a higher requirement for heat dissipation.

Monomer batteries more and more like tesla so many batteries, to the management system requirements is large, and there is no way to monitor multiple, so now slowly to monomer batteries capacity requirements, quantity increase the convenience of management, can reduce the surface area, the same volume of batteries, large batteries, as long as a space, radiating surface limited, if quantity radiating surface can be increased, Such batteries will appear within a local high temperature, about batteries is laminated now, if the thickness, the greater the batteries batteries guideline to the shell surface, the distance, the greater the difference in temperature is, the greater the fold for batteries through a layer of a layer of anode diaphragm, after the heat conduction path, path of thermal conductivity with metal and some other chemical materials, coefficient of thermal conductivity is not the same. This is also the case where we say that the performance of a battery as a whole is not consistent with the thermal conductivity of the longitudinal and horizontal vertical directions.

Control thermal management important goal is to make the batteries in the appropriate temperature range, the temperature difference between the control inside the PACK will now properly know about 5 degrees should be controlled in the following, in addition the processing of thermal runaway, it is high temperature and high pressure conditions, how to put the high temperature and high pressure gas drainage, don't let it affect other batteries, it should also be a task of thermal management.

At present, the means of thermal management, in fact, thermal management is a treatment of heat, heat treatment either heat dissipation or heating or insulation, exhaust design is important to pin on the heat out of control when a high pressure airflow shunt or a pressure limit.

Because of the whole new energy, I learned that the national standard should prevent toxic gas from entering the passenger compartment, how to design the explosion-proof valve and how to import toxic gas into the outside. Thermal management should understand, since it is the heat treatment, how come, thermal batteries is a part of the heat production, according to the difference of its emergence, several aspects, one is the electrochemical reflect heat it is reversible, and electrochemical vice reflect heat, the situation is less, and joule heat, exists, and is due to the melting degree of polarization of a hot, under normal circumstances, In the specifications of the batteries we use the standard case this is the dominant, if the process of thermal runaway, the dominant is electrochemical side effects, why put the batteries in a temperature control, high temperature limit, the high temperature should not be put forward by hot actually, should be what batteries are suggested, because batteries, electrochemical process, To a certain extent what will happen to the material here, I change what is endothermic or exothermic heat caused by the change of heat, resulting in the next stage of the occurrence, this is the cell has more say.

Joule heat is a large magnification, why do the cell do different magnification, heat is not the same as we imagine the rise. In addition, it is electrical heat generation, which is basically the busbar. Other electronic components generally have high voltage and this aspect. If they are integrated in it, it depends on what electronic components are arranged, which may cause you to have partial high temperature in the whole PACK.

This one is to consider the simulation process, because of new to this area, I do a simulation through the calorific value of batteries, to the place I there are differences between the simulation results with the actual test results, consult the relevant experience is enough people behind, they explained to me, may be missing the electrical output has not taken into account.

So, some of the work that this whole thermal management does is solve the task that I just said, what is the knowledge? These knowledge personally, I think, since it is thermal management engineer, engineer is a more extensive, may want to contact a lot of things, not only is your specialty and adjacent, the core point, thermal production and also to thermal and fluid mechanics, with the development of the computer, including the development cycle shortened, thermal simulation computation fluid dynamics will, these is a basic, On this basis for us to do is the electric core, the electric core is not a physical thing, is the knowledge of electrical transformation.

The second part is the cooling and heating technology, cooling these you can search on the net, actually all is very simple, common according to the structure of natural cooling, the power lithium battery pack cool in this concept may be wrong, there is also a air cooling, cold, surface and so on, the more common is air-cooled, cools, straight cold, use refrigerant heat in direct contact with the batteries.

Natural cooling is called passive cooling are appropriate, since it is air cooling is low temperature air as medium, so the mean is not applying auxiliary power for cooling, and only use the speed of the wind cooling for battery, I didn't do it the natural air cooling test, this is my understanding, important is to put the heat conduction to the other a component, and the shell of the heat dissipation, If battery pack below enclosed, is equal to the heat conductivity of the battery to the shell, encapsulating the wind without battery pack shell is natural cooling, the thermal conductivity on pure air, in this case, the remaining basic thermal coefficient is very low, normal convection coefficient between 5 and 25 v, this time very little heat, heat can only rely on the absorption of other components.

Characteristic is simple structure, simple control, according to my idea is to cloth a point, the cost is relatively low, it is very easy to do sealing.

The disadvantage is uncontrolled, the temperature is not dry, less heat dissipation, this design point of this method design point, I think one is my cell to spread the heat to the outside, scattered to other components, how to get through the heat conduction path.

If I talk about how to design the appearance of the shell of the package in contact with the gas and how to make the heat dissipate faster in the process of use, there is a leakage here. There is an important point that the heat of my battery core should not be too high. Once the heat is too high, it is difficult to deal with this problem.

Other air cooling is also called active air-cooled or forced cooling, is to use the fan with a car bring evaporator, our normal car, car air conditioning evaporator is to the passenger compartment air down, here the passenger compartment like this way the passenger compartment of a cryogenic gas led to the bag inside, this kind of situation is certainly no way do we require seal grade, And because it is in direct contact with the outside air, it is difficult to control incoming dust or contaminants to the battery components.

And forced air cooling on abortion heat coefficient in tens of, the cooling effect is not very good. In this way, it is relatively simple. I just need to set a fixed pipeline and add a fan, maybe one or several, as long as the gas is brought in and discharged. The cost is relatively low, but the advantage is that the temperature can be controlled, because it is a gas in the passenger cabin. 

In the design process of air cooling, there are not many components designed, such as a fan and an air duct. The fan is basically a key point, and the design of the air duct. Because there are many batteries in the battery pack, how to control the temperature of these batteries within the allowable range?

The selection of the fan, the first must know how much I want an air volume, the previous may use the most original relevant experience company calculate the number of air duct pressure frame, now make the model, adjust the boundary of the inlet, different corresponding different pressure frame, directly put it into this to do. The simulation is to get a system pressure loss curve with the performance curve of the fan. The fan is usually low-voltage electricity. In fact, it is not easy to choose an inlet pressure and air volume. I missed a point in the front. In the normal process we use, the type of fan is important for penetration and centrifugation, which is basically not used in this respect. Basically, it is either turbidity current. Because less air heat to dissolve, if the wind, the control of a road is long, will pull the temperature difference is very big, before and after the mentioned temperature difference is very important for a package, so do a flow, how to let each batteries, drainage, air volume is more or less, or even how to shorten the air of a forward path length.

In addition, liquid cooling, we now use more, according to its structure can be divided into several, one is a low temperature radiator cooling system, a direct cooling system, and mixed liquid cooling.

First, the cooling water inside the battery is directly radiated with the environment inside.

The second, more commonly used is the direct cooling water cooling system, because this is equivalent to the heat of my battery to the cooling water of the battery, the heat is transferred to the refrigerant through the cooling water, and then the heat is transferred to the air through the refrigerant.

Third, combine the advantages of the previous two.

The first low temperature radiator in high temperature is not good to do, the external environment temperature is high, the temperature of cooling water is not controlled.

Second, direct cooling water can ensure cooling water through the refrigerant system, such as 35 degrees, 15 degrees of cooling water, 45 degrees of cooling water can also be achieved. This is equivalent to better management of the system.


Mixed in the case of low temperature outside, with the first low temperature radiator cooling system, does not enter the refrigerant system of the cross, this is a comprehensive environmental adaptability has a energy consumption aspect, the cost is obviously higher than the previous two.

The first kind, the cost is relatively low, as long as a pump other do not consider.

Second, a battery cooler. In the process of water cooling can be involved in some things, one is the pump and heat exchanger plate, a pump selection is easier to do, the most important battery pack cooler. This contact with the cell and how to control the flow can also follow the wind can encounter the same problem, how to do the cell through the flow of water, or I with the flow and calorific relationship, how to do this is a more troublesome thing. Because I can do a lot, the more momentum I have, the less flow I have, because my pump has an energy problem. So how to comprehensively evaluate this problem, I think we can only rely on simulation run, first put forward the method, first to work out the general idea, and then how do you feel.

I have never touched power lithium battery. I used to work in air conditioning before I did air conditioning. Later, I switched to this field, and I am very interested in this field.

The direct cooling system, the direct refrigerant cooling of the battery, the whole system consists of the compressor and the refrigerant and an electromagnetic expansion method. This feature compared to the surface, at least, to eliminate the water cooling system of a component, including a loss of energy consumption, relatively structure is more compact, lighter weight, the data had been done, efficiency is high, the water pump power consumption is lower, because refrigerant do a pressure or larger, and we have no way to do it as thick as the original car air conditioning do, One of my high voltage scour on the loss of the pipeline components of the loss of more trouble.

In addition, because of what we do is a phase change, it's hard to control the state of a refrigerant, can form some kind of gas and liquid or is completely liquid, even is the degree of supercooling, such as water, the same has been lower than zero, so I only have the temperature rises to zero phase change process, this we will involve things, one is we understand through high too cold, cold media after the first battery, It is equivalent to using sensible heat overheating. In this case, the amount of heat absorbed is more, and the heat is relatively low. It is difficult to control the temperature difference of the whole package.

In addition, heating is more difficult, because originally I have always thought to reverse this, the evaporator into the refrigerant, because the two heat exchange is not the same, the area of the heat exchanger is not the same, if I am suitable for an evaporator to take an area, the refrigerant may not be so more difficult.

The key points of the design are the components involved. One is the compressor, expansion pipe and pipeline design, which are the same as the low-temperature design. How to distribute the flow includes how to control it.

According to the battery pack evaporator and the vehicle evaporator, it is important to be independent, parallel and series. The independent system and the automobile air conditioning system not only have high cost and relatively large energy consumption, provided that you exceed the cooling capacity, because not only one more compressor but also one more condensing agent.

In addition, there is also a problem in series. The car air conditioner basically has a low temperature, which should be about 10 degrees with the household air conditioner. In this case, the gas coming out through the cold plate may cause different demand for a cooling capacity behind it.

Through the same compressor in parallel, the refrigerant state out of the vehicle is consistent with the state out of the battery. This one is also more difficult to control.

In addition, a selection of the design, because of the time relationship, the compressor in this will involve a lubricating oil problem, usually, the smaller your pipe wall, the better the oil return ability to bring back the oil, resulting in new pressure loss.

Heating and insulation technology, in fact, I really did not find any new technology, basically heating film, PTC, water heating, water heating heater, heating aluminum plate.

Thermal insulation method: there are some materials isolated, using low thermal conductivity technical materials, in addition through the air, now the material like aerogel leads to little difference between the coefficient and the air, the problem of cell structure.

At home and abroad of the status quo of surface is the mainstream now, in addition to Japan, I don't understand, why they are looking for air cooled so, there are some Europe will there is a demand for straight cold, now many western high voltage platform, once made equivalent to a ratio of current fast charge demand is lower, whether do air-cooled chiller and natural.

This is the bank of China securities to comb, the mainstream of new energy vehicles at home and abroad is indeed a surface more, like is six 10 domestic car liquid-cooled, abroad is 6 only two is air cooled, the other is also cools, there is a time lag, doing design for vehicle, get in the car and the methods of doing now may be a time some or do some air.

The market for thermal management is now what they call the blue ocean and they have a prediction that the market for thermal management is going to grow, both domestically and internationally. Suppliers like the top four in the entire automotive thermal management industry, comprising 55%. In the thermal management segment of new energy vehicles, there are three types of companies, one is the international giants of traditional thermal management vehicles, some leading domestic thermal management companies, and some emerging companies, which have been exposed to them earlier.

Nissan's Leaf side there are a lot of papers about actually, I don't speak, I don't understand, that I have seen apart video, according to my ideas, should put the heat conduction through the contact between modules is to do the processing of boundary, the metal under the two bolt tightening, here are a one of the modules of the tray can have a heat conduction, batteries apart inside, I only see the upper and lower end faces, thermal conductivity silica gel and silica gel electricity, how the heat conduction in the middle is a little unclear. I see that the heat conduction should be carried out through contact between aluminum foil and aluminum foil. The heat conduction silicone pad, including the metal shell, has a concave design, and the important design is the bulging of the needle.

This cell is made thinner by 8 mm, and the soft pack has three directional import technology, like the vertical direction of one with very low thermal conductivity, because of the different positive and negative poles mentioned before.

And the Chevrolet Bolt, the little plate piping design, I looked it up on the Internet, it's kind of like a direct cooling system, where one module goes through a high temperature and a low temperature, so it's temperature consistency.

I'm curious about a management strategy of Tesla, but I can't find relevant materials, so I won't talk about it after what General Manager Sun mentioned before.

As for Jaguar, have you noticed that these two materials are supplied by them? I will not repeat them. They have more information and materials.

BMW i3's straight cooling, low temperature and high temperature are two average pairs of temperature soaking. The i3 has a herringbone shaped rubber underneath to keep it in close contact with the battery.

Finally the prospect of thermal management technology, the application of phase change materials, which are frequently used now including the phase change materials abroad do, they use graphite and wax, the use of a field is 48 the battery, because of the high ratio calorific value is big, there is no way to do a lot of heat and no way to do a set of cooling system, phase change materials to a phase transition point, to absorb the heat.

In addition, foreign minister change material as a cylindrical thermal runaway is good, because I don't understand thermal runaway is important if I put the heat as the heat, in the beginning to feel the heat consumption, but there is no way affect the other, or two, a let you bear the risk, insulation and are cold and the thermal runaway, phase change materials absorb heat transfer to the other, Overall, we're still keeping the temperature. The other one is semiconductor cooling, which is used for in-car refrigerators, and I don't know how to use it for power lithium-ion batteries, but somebody's working on it.

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